diff --git a/CMakeLists.txt b/CMakeLists.txt
index 36714d7..ca958ae 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -4,6 +4,7 @@ set(CMAKE_CXX_STANDARD_REQUIRED True)
 
 project(ChonkyStation)
 add_subdirectory(external)
+add_subdirectory(test)
 add_subdirectory(src)
 
 include_directories(src/common)
@@ -14,14 +15,17 @@ include_directories(src/gpu)
 include_directories(src/cdrom)
 include_directories(src/scheduler)
 
+include_directories(test)
+
 include_directories(external/Dolphin)
 include_directories(external/Panda3DS)
 
+source_group("Header Files/Test" FILES ${TEST_HEADER_FILES})
 source_group("Header Files/External/Dolphin" FILES ${DOLPHIN_HEADER_FILES})
 source_group("Header Files/External/Panda3DS" FILES ${PANDA3DS_HEADER_FILES})
 
 add_compile_definitions(SDL_MAIN_HANDLED)
 
-add_executable(ChonkyStation ${SOURCE_FILES} ${HEADER_FILES} ${DOLPHIN_HEADER_FILES} ${PANDA3DS_HEADER_FILES})
+add_executable(ChonkyStation ${SOURCE_FILES} ${HEADER_FILES} ${TEST_SOURCE_FILES} ${TEST_HEADER_FILES} ${DOLPHIN_HEADER_FILES} ${PANDA3DS_HEADER_FILES})
 target_include_directories(ChonkyStation PRIVATE ${SDL2_INCLUDE_DIR})
 target_link_libraries(ChonkyStation PRIVATE fmt SDL2-static)
\ No newline at end of file
diff --git a/src/cpu/backends/interpreter/interpreter.cpp b/src/cpu/backends/interpreter/interpreter.cpp
index 766dc3e..3db77a9 100644
--- a/src/cpu/backends/interpreter/interpreter.cpp
+++ b/src/cpu/backends/interpreter/interpreter.cpp
@@ -1,8 +1,8 @@
 #include "interpreter.hpp"
 
 
-//#define DONT_CRASH_ON_BAD_READWRITE
-//#define DONT_CRASH_ON_BAD_JUMP
+#define DONT_CRASH_ON_BAD_READWRITE
+#define DONT_CRASH_ON_BAD_JUMP
 
 void Interpreter::step(CpuCore* core, Memory* mem, Disassembler* disassembler) {
 	// Handle interrupts
diff --git a/src/cpu/backends/old_interpreter/old_interpreter.cpp b/src/cpu/backends/old_interpreter/old_interpreter.cpp
index 6265010..61312ce 100644
--- a/src/cpu/backends/old_interpreter/old_interpreter.cpp
+++ b/src/cpu/backends/old_interpreter/old_interpreter.cpp
@@ -68,6 +68,7 @@ void OldInterpreter::step(CpuCore* core, Memory* mem, Disassembler* disassembler
 	if (delay) {	// branch delay slot
 		core->pc = jump - 4;
 		delay = false;
+		core->isDelaySlot = false;
 	}
 
 	// Quick and dirty hack. TODO: Replace this with a bitfield
@@ -125,6 +126,7 @@ void OldInterpreter::step(CpuCore* core, Memory* mem, Disassembler* disassembler
 			jump = addr;
 			debug_log("jr %s\n", reg[rs].c_str());
 			delay = true;
+			core->isDelaySlot = true;
 			break;
 		}
 		case 0x09: {
@@ -137,6 +139,7 @@ void OldInterpreter::step(CpuCore* core, Memory* mem, Disassembler* disassembler
 			jump = addr;
 			debug_log("jalr %s\n", reg[rs].c_str());
 			delay = true;
+			core->isDelaySlot = true;
 			break;
 		}
 		case 0x0C: {
@@ -304,6 +307,7 @@ void OldInterpreter::step(CpuCore* core, Memory* mem, Disassembler* disassembler
 			if (signed_rs < 0) {
 				jump = (core->pc + 4) + (sign_extended_imm << 2);
 				delay = true;
+				core->isDelaySlot = true;
 				debug_log(" branched\n");
 			}
 			else { debug_log("\n"); }
@@ -315,6 +319,7 @@ void OldInterpreter::step(CpuCore* core, Memory* mem, Disassembler* disassembler
 			if (signed_rs >= 0) {
 				jump = (core->pc + 4) + (sign_extended_imm << 2);
 				delay = true;
+				core->isDelaySlot = true;
 				debug_log(" branched\n");
 			}
 			else { debug_log("\n"); }
@@ -326,6 +331,7 @@ void OldInterpreter::step(CpuCore* core, Memory* mem, Disassembler* disassembler
 		jump = (core->pc & 0xf0000000) | (jump_imm << 2);
 		debug_log("j 0x%.8x\n", jump_imm);
 		delay = true;
+		core->isDelaySlot = true;
 		break;
 	}
 	case 0x03: {
@@ -333,6 +339,7 @@ void OldInterpreter::step(CpuCore* core, Memory* mem, Disassembler* disassembler
 		debug_log("jal 0x%.8x\n", jump_imm);
 		regs[0x1f] = core->pc + 8;
 		delay = true;
+		core->isDelaySlot = true;
 		break;
 	}
 	case 0x04: {
@@ -340,6 +347,7 @@ void OldInterpreter::step(CpuCore* core, Memory* mem, Disassembler* disassembler
 		if (regs[rs] == regs[rt]) {
 			jump = (core->pc + 4) + (sign_extended_imm << 2);
 			delay = true;
+			core->isDelaySlot = true;
 			debug_log(" branched\n");
 		}
 		else { debug_log("\n"); }
@@ -350,6 +358,7 @@ void OldInterpreter::step(CpuCore* core, Memory* mem, Disassembler* disassembler
 		if (regs[rs] != regs[rt]) {
 			jump = (core->pc + 4) + (sign_extended_imm << 2);
 			delay = true;
+			core->isDelaySlot = true;
 			debug_log(" branched\n");
 		}
 		else { debug_log("\n"); }
@@ -360,6 +369,7 @@ void OldInterpreter::step(CpuCore* core, Memory* mem, Disassembler* disassembler
 		if (signed_rs <= 0) {
 			jump = (core->pc + 4) + (sign_extended_imm << 2);
 			delay = true;
+			core->isDelaySlot = true;
 			debug_log(" branched\n");
 		}
 		else { debug_log("\n"); }
@@ -370,6 +380,7 @@ void OldInterpreter::step(CpuCore* core, Memory* mem, Disassembler* disassembler
 		if (signed_rs > 0) {
 			jump = (core->pc + 4) + (sign_extended_imm << 2);
 			delay = true;
+			core->isDelaySlot = true;
 			debug_log(" branched\n");
 		}
 		else { debug_log("\n"); }
diff --git a/src/gpu/gpu.cpp b/src/gpu/gpu.cpp
index f931462..b1e57ca 100644
--- a/src/gpu/gpu.cpp
+++ b/src/gpu/gpu.cpp
@@ -54,6 +54,11 @@ void GPU::writeGp0(u32 data) {
 	if (paramsLeft == 0) {
 		if (!uploadingTexture) {
 			switch (fifo[0] >> 24) {
+			case (u32)GP0Command::FillVRAM: {
+				// TODO
+				hasCommand = false;
+				break;
+			}
 			case (u32)GP0Command::UploadTexture: {
 				uploadingTexture = true;
 				// Calculate size
@@ -145,17 +150,23 @@ void GPU::writeGp0(u32 data) {
 						vert.u = fifo[idx] & 0xff;
 						vert.v = (fifo[idx++] >> 8) & 0xff;
 					}
-					// TODO: variable size
-					Helpers::debugAssert(rect.size != 0, "[FATAL] Unimplemented variable size rectangle\n");
+
 					// TODO: textured
 					Helpers::debugAssert(!rect.textured, "[FATAL] Unimplemented textured rectangle\n");
 
 					u16 width = 0;
 					u16 height = 0;
-					switch (rect.size) {
-					case 1: width =  1; height =  1; break;
-					case 2: width =  8; height =  8; break;
-					case 3: width = 16; height = 16; break;
+
+					if (rect.size == 0) {
+						width = fifo[idx] & 0xffff;
+						height = (fifo[idx++] >> 8) & 0xffff;
+					}
+					else {
+						switch (rect.size) {
+						case 1: width = 1; height = 1; break;
+						case 2: width = 8; height = 8; break;
+						case 3: width = 16; height = 16; break;
+						}
 					}
 
 					backend->drawRectUntextured(vert, width, height);
@@ -248,6 +259,12 @@ void GPU::startCommand(u32 rawCommand) {
 		// Stubbed
 		break;
 	}
+	case (u32)GP0Command::FillVRAM: {
+		log("FillVRAM\n");
+		paramsLeft = 2;
+		hasCommand = true;
+		break;
+	}
 	case (u32)GP0Command::UploadTexture: {
 		log("UploadTexture\n");
 		paramsLeft = 2;
diff --git a/src/gpu/gpu.hpp b/src/gpu/gpu.hpp
index 53ec81c..0196536 100644
--- a/src/gpu/gpu.hpp
+++ b/src/gpu/gpu.hpp
@@ -42,6 +42,7 @@ public:
 	enum class GP0Command {
 		NOP							= 0x00,
 		ClearCache					= 0x01,
+		FillVRAM					= 0x02,
 		UploadTexture				= 0xA0,
 		ReadVRAM					= 0xC0,
 		DrawModeSetting				= 0xE1,
diff --git a/src/main.cpp b/src/main.cpp
index 936a60d..9e51cfe 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -2,6 +2,8 @@
 #include <SDL.h>
 #include "playstation.hpp"
 
+#include <diff/diff.hpp>
+
 
 int main(int argc, char** argv) {
     if (argc < 2) Helpers::panic("Usage: ChonkyStation [bios path]\n");
@@ -14,6 +16,10 @@ int main(int argc, char** argv) {
         playstation.sideloadExecutable(argv[2]);
     }
 
+    // Testing
+    //Test::Diff diffTest = Test::Diff(argv[1]);
+    //diffTest.doTest();
+
     // SDL Window
     SDL_Init(SDL_INIT_VIDEO);
     SDL_Window* window = SDL_CreateWindow("ChonkyStation", 100, 100, 1024, 512, 0);
diff --git a/src/memory/memory.cpp b/src/memory/memory.cpp
index a95bcda..36c00f9 100644
--- a/src/memory/memory.cpp
+++ b/src/memory/memory.cpp
@@ -157,6 +157,9 @@ u32 Memory::read(u32 vaddr) {
 	else if (paddr == 0x1f8010f4) return dma->dicr;
 	// Timers
 	else if (Helpers::inRangeSized<u32>(paddr, (u32)MemoryBase::Timer, (u32)MemorySize::Timer)) return 0;
+
+	else if (paddr == 0x1f80101C) return 0x00070777;	// Expansion 2 Delay/Size (usually 00070777h) (128 bytes, 8bit bus)
+
 	else
 		Helpers::dump("ramdump.bin", ram, 2_MB);
 		Helpers::panic("[  FATAL  ] Unhandled read32 0x%08x (virtual 0x%08x) @ pc 0x%08x\n", paddr, vaddr, core->pc);
diff --git a/src/playstation.hpp b/src/playstation.hpp
index 554d195..44726d5 100644
--- a/src/playstation.hpp
+++ b/src/playstation.hpp
@@ -16,7 +16,7 @@ public:
         mem.core = &cpu.core;
 
         mem.loadBios(biosPath);
-        cpu.switchBackend(Cpu::Backend::Interpreter);
+        cpu.switchBackend(Cpu::Backend::OldInterpreter);
 
         // Setup GPU scheduler events
         scheduler.push(&gpu.scanlineEvent, scheduler.time + GPUConstants::cyclesPerScanline, &gpu);
@@ -47,6 +47,7 @@ public:
     u32 getPC() { return cpu.core.pc; }
     u8* getRAM() { return mem.ram; }
     u8* getVRAM() { return gpu.getVRAM(); }
+    u32* getGPRS() { return cpu.core.gprs; }
     bool getVBLANKAndClear() {
         bool temp = gpu.vblank;
         gpu.vblank = false;
@@ -55,6 +56,8 @@ public:
     void VBLANK() { interrupt.raiseInterrupt(Interrupt::InterruptType::VBLANK); }
     bool isInBIOS() { return Helpers::inRangeSized<u32>(cpu.core.pc, (u32)Memory::MemoryBase::BIOS, (u32)Memory::MemorySize::BIOS); }
     
+    void switchCpuBackend(Cpu::Backend backend) { cpu.switchBackend(backend); }
+
     void loadExecutable(const fs::path path) {
         auto binary = Helpers::readBinary(path);
 
diff --git a/test/CMakeLists.txt b/test/CMakeLists.txt
new file mode 100644
index 0000000..6bb9360
--- /dev/null
+++ b/test/CMakeLists.txt
@@ -0,0 +1,7 @@
+set(TEST_SOURCE_FILES
+"${CMAKE_CURRENT_SOURCE_DIR}/diff/diff.cpp"
+PARENT_SCOPE)
+
+set(TEST_HEADER_FILES
+"${CMAKE_CURRENT_SOURCE_DIR}/diff/diff.hpp"
+PARENT_SCOPE)
\ No newline at end of file
diff --git a/test/diff/diff.cpp b/test/diff/diff.cpp
new file mode 100644
index 0000000..e10ccdc
--- /dev/null
+++ b/test/diff/diff.cpp
@@ -0,0 +1,38 @@
+#include "diff.hpp"
+
+
+using namespace Test;
+
+Diff::Diff(const fs::path& biosPath) : p1(biosPath), p2(biosPath) {
+	p1.switchCpuBackend(Cpu::Backend::Interpreter);
+	p2.switchCpuBackend(Cpu::Backend::OldInterpreter);
+}
+
+void Diff::doTest() {
+	u32* gprs1 = p1.getGPRS();
+	u32* gprs2 = p2.getGPRS();
+
+	while (true) {
+		while (!p1.getVBLANKAndClear()) {
+			p1.step();
+			p2.step();
+
+			for (int i = 0; i < 32; i++) {
+				if (gprs1[i] != gprs2[i]) {
+					printf("r%d | 0x%08x != 0x%08x\n", i, gprs1[i], gprs2[i]);
+					exit(0);
+				}
+			}
+
+			if (p1.getPC() != p2.getPC()) {
+				printf("pc | 0x%08x != 0x%08x\n", p1.getPC(), p2.getPC());
+				
+				Helpers::dump("ramp1.bin", p1.getRAM(), 2_MB);
+				Helpers::dump("ramp2.bin", p2.getRAM(), 2_MB);
+				exit(0);
+			}
+		}
+		p1.VBLANK();
+		p2.VBLANK();
+	}
+}
\ No newline at end of file
diff --git a/test/diff/diff.hpp b/test/diff/diff.hpp
new file mode 100644
index 0000000..9d77151
--- /dev/null
+++ b/test/diff/diff.hpp
@@ -0,0 +1,16 @@
+#pragma once
+
+#include <helpers.hpp>
+#include "../../src/playstation.hpp"
+
+
+namespace Test {
+	class Diff {
+	public:
+		Diff(const fs::path& biosPath);
+		void doTest();
+	private:
+		PlayStation p1;
+		PlayStation p2;
+	};
+}	// End namespace test
\ No newline at end of file